Methods and apparatus to repair a rotor disk for a gas turbine

ABSTRACT

Embodiments of the invention can provide methods and apparatus to repair a rotor disk for a gas turbine. In one embodiment, a method to repair a rotor disk for a gas turbine is provided, wherein the rotor disk can include a base and at least one dovetail slot between a pair of dovetail walls. The method can include identifying one or more cracks on the base of the rotor disk, and removing one or more cracks by providing one or more fillets on the base of the rotor disk. Further, the method can include providing one or more conic cuts on the base of the rotor disk between the pair of dovetail walls of at least one dovetail slot.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to a gas turbine, and more particularly,methods and apparatus to repair a rotor disk for a gas turbine.

2. Description of the Related Art

Generally, a compressor rotor wheel assembly of a gas turbine caninclude a rotor disk and a plurality of rotor blades. The rotor disk canbe provided with a plurality of dovetail slots around its periphery andeach of the plurality of rotor blades are provided with a dovetail. Thedovetail of each of the plurality of rotor blades can be axiallyinserted in one of the plurality of dovetail slots of the rotor disk tocomplete the compressor rotor wheel assembly. In some instances, theapplication of such a compressor rotor wheel assembly is not limited togas turbines. The compressor rotor wheel assembly can also be used inother power generation and thrust generation applications.

After the rotor disk is installed into the gas turbine, a forward sideand an aft side can be defined according to the direction of flow of aworking fluid. The working fluid in the gas turbine can enter from theforward side of the rotor disk and escapes from the aft side of therotor disk. Further, each of the plurality of dovetail slots of therotor disk can include a pair of dovetail walls and a base of the rotordisk. Each of the plurality of dovetail slots can include a plurality ofacute corners located on the base of the rotor disk on the forward andthe aft sides of the rotor disk.

During operational conditions, the high rotational speed of the rotordisk and/or thermal gradients can cause the plurality of acute cornersto experience high tangential and radial stresses, which may cause aninitiation of one or more cracks at the plurality of acute corners ofthe plurality of dovetail slots. Further, each crack may increase as therotor disk is in operation.

Conventional methods for repairing a rotor disk for a gas turbine relateto cracks having a length of less than about 0.1 inches (2.5 mm).However, in case the length of a crack is greater than about 0.1 inches(2.5 mm), no repair option is defined, and the rotor disk may bescrapped.

Scrapping the rotor disk can directly increase the operational cost of agas turbine due to the downtime and/or service time needed todisassemble the associated turbine and remove the rotor disk. In lightof the above, there is need for a repair methodology of a rotor diskhaving one or more cracks with the length greater than about 0.1 inches.Furthermore, there exists a need for methods and apparatus to repair arotor disk for a gas turbine.

BRIEF DESCRIPTION OF THE INVENTION

Some or all of the needs above can be addressed by embodiments of theinvention. Embodiments of the invention can provide methods andapparatus to repair a rotor disk for a gas turbine. In one embodiment, amethod is provided for repairing a rotor disk for a gas turbine, whereinthe rotor disk can include a base and at least one dovetail slot betweena pair of dovetail walls. In this embodiment, one or more cracks can beidentified on the base of the rotor disk. The identified one or morecracks can be removed and one or more fillets can be provided on thebase of the rotor disk. Further, one or more conic cuts can be providedon the base of the rotor disk between the pair of dovetail walls of theat least one dovetail slot.

In another embodiment of the invention, a method is provided whichpermits reuse of a rotor disk in a gas turbine. The method can includeidentifying one or more cracks having a length greater than about 0.1inches (2.5 mm) and within about 0.25 inches (6.4 mm) on the base of arotor disk. The identified one or more cracks can be removed from thebase of the rotor disk and one or more fillets can be provided on thebase. Radii of one or more fillets provided on the base can be about 0.1inches (2.5 mm). Further, one or more conic cuts with a rho value (alsocalled projective discriminant) less than about 0.5 can be providedbetween the pair of dovetail walls of the at least one dovetail slot. Adepth of one or more conic cuts can be about 0.45 inches (11.4 mm) andthe corresponding length of one or more conic cuts can be about 0.55inches (14.0 mm) in dimension.

In another embodiment of the invention, an apparatus to repair a rotordisk for a gas turbine can be provided, wherein the rotor disk caninclude a base and at least one dovetail slot between a pair of dovetailwalls. The apparatus can include one or more fillets on the base,wherein one or more cracks are removed from the base of the rotor disk.Further, one or more conic cuts can be provided on the rotor diskbetween the pair of dovetail walls of the at least one dovetail slot,wherein one or more conic cuts can include a rho less than about 0.5.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be discussed in more detail withreference, by way of example, to the accompanying drawings, in which:

FIG. 1 illustrates a portion of an example rotor disk of a gas turbine.

FIG. 2 is an example view of a at least one dovetail slot of the rotordisk of FIG. 1, and one or more example cracks at the base of the atleast one dovetail slot.

FIGS. 3 a-3 e are example views of the at least one dovetail slot withthe one or more fillets and the one or more conic cuts on the rotor diskin accordance with an embodiment of the invention.

FIGS. 4 a-4 b illustrate an example geometry of the one or more coniccuts provided between the pair of dovetail walls of the at least onedovetail slot of the rotor disk in accordance with an embodiment of theinvention.

FIG. 5 illustrates an example method for repairing a rotor disk inaccordance with an embodiment of the invention

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a portion of an example rotor disk 100 of a gasturbine. The rotor disk 100 can include a base 102 and at least onedovetail slot 104 for attaching a rotor blade. Typically, the rotor diskincludes multiple rotor blades or an array of rotor blades. The rotorblades are provided with a respective dovetail, which can be axiallyinserted into the at least one dovetail slot 104 to fit the rotor bladesin the rotor disk 100. During operation of the gas turbine, the rotordisk 100 can rotate about an axial direction 106. Further, the rotordisk 100 can include a forward side 112 and an aft side. In an aspect ofthe invention, a working fluid in a compressor rotor wheel assembly canenter an associated array of rotor blades from the forward side 112 ofthe rotor disk 100 and can escape from the array from the aft side ofthe rotor disk 100.

In an embodiment of the invention, the rotor disk 100 can be used in acompressor rotor wheel assembly of a gas turbine. However, applicationsof a rotor disk 100, are not limited to a compressor rotor wheelassembly of a gas turbine, but can be used other applications such as inpower generation and thrust generation.

FIG. 2 is an example view of at least one dovetail slot 104 of the rotordisk 100 shown in FIG. 1. Each of the dovetail slots 104 of the rotordisk 100 can include a pair of dovetail walls 202 a and 202 b. A portionof the base 102 of the rotor disk 100 can be seen in FIG. 2, wherein thebase 102 can include a width 204 and depth 205. Each of the dovetailslots 104, thus can include a base portion which can collectively beknown as the base 102. Further, the base 102 can extend along thecircumference of the rotor disk 100. FIG. 2 also shows a plurality ofacute corners 206 formed at the forward side 112 and the aft side whereeach pair of dovetail walls 202 a and 202 b can meet the base 102.

During operation of the rotor disk 100, the plurality of acute corners206 may experience high tangential and radial stresses, which may causeone or more cracks, 208. Cracks 208 may appear after a certain number ofoperational cycles (start-up and/or rotation during operation) of therotor disk 100. The number of operational cycles after which a crack 208may begin to appear is known as crack initiation life. After the crackinitiation life, a length ‘C’ of the crack 208 can continuously increasewith the number of operational cycles and thus the length ‘C’ of thecrack 208 may depend upon, or otherwise be based at least in part on thenumber of operational cycles occurring after the crack initiation lifeand before the inspection of the rotor disk 100 to identify the crack208. In some instances, a length ‘C’ of a crack 208 may extend in one ormore other directions, including upward, laterally, and downward.

FIGS. 3 a-3 e are example views of a dovetail slot 104 with one or morefillets 302, and one or more conic cuts 304. FIG. 3 e represents radii‘ΦR’ and an axially extending depth ‘L1’ of at least one fillet 302.FIGS. 3 b, 3 c and 3 d are example views of at least one dovetail slot104 taken from different angles to illustrate an example shape of one ormore fillets 302, and one or more conic cuts 304.

In an embodiment of the invention, a method is provided for repairing ofa rotor disk 100 with the one or more cracks 208. In one aspect of theinvention, one or more cracks 208 can be identified on a plurality ofacute corners 206 of a forward side 112 of the base 102 of the rotordisk 100. Further, the length ‘C’ of the cracks 208 may be greater thanabout 0.1 inches (2.5 mm) and less than or otherwise within about 0.25inches (6.4 mm). The phrase “about 0.25 inches (6.4 mm)” is intended toinclude dimensions up to about 0.30 inches (7.6 mm). In some instances,the length ‘C’ of the cracks 208 can extend in one or more directions,including upward, laterally, and downward. Subsequently, one or morecracks 208 can be removed across a portion of the width 204 and/or depth205 of the base 102 on the forward side 112 of the rotor disk 100 toprovide one or more fillets 302. One or more fillets 302 can be providedacross the portion of the width 204 and/or depth 205 of the base 102along the circumference of the rotor disk 100. In an aspect of theinvention, one or more fillets 302 can generally be round shaped andproviding one or more fillets 302 on the base 102 of the rotor disk 100can include providing one or more fillets 302 with a radii ‘ΦR’ of about0.1 inches (2.5 mm), and a depth ‘L1’ between about 0.1 inches (2.5 mm)to about 0.25 inches (6.4 mm). However the radii ‘ΦR’ and the depth ‘L1’of one or more fillets 302 need not be limited to these values, as onecan suitably select a radii ‘ΦR’ and a depth ‘L1’ of one or more fillets302 as per the applications of a compressor rotor wheel assembly toremove cracks 208, in accordance with an embodiment of the invention.Further, one or more conic cuts 304 can be provided between the pair ofdovetail walls 202 a and 202 b of the dovetail slot 104 on the forwardside 112 of the base 102 of the rotor disk 100. In an aspect of theinvention, one or more conic cuts 304 can be provided on both theforward side 112 and the aft side of the base 102 of the rotor disk 100.An example shape of one or more conic cuts 304 is explained and shown indetail with respect to FIGS. 4 a-4 b.

Referring now to FIGS. 4 a-4 b, an example geometry of one or more coniccuts 304 provided between a pair of dovetail walls 202 a and 202 b of atleast one dovetail slot 104 of the rotor disk 100 is shown in accordancewith an embodiment of the invention. FIG. 4 a illustrates the top viewof one or more conic cuts 304, and FIG. 4 b illustrates the examplegeometry of one or more conic cuts 304. FIG. 4 a also illustrates adepth ‘D’ and a length ‘L’ of one or more conic cuts 304. The solid linein FIG. 4 b represents a conic curve 402 and the end points of the coniccurve 402 are called a start edge curve 404 and an end edge curve 406.The respective dotted lines originating from the start edge curve 404and the end edge curve 406 represent the tangents at these points andthey meet at a point known as an apex curve 408. Further, the directionalong the straight line joining the start edge curve 404 and the endedge curve 406 is called an x-axis 410 and the direction perpendicularto the x-axis 410 is called a y-axis 412. A distance D1 of a vertex 416can be defined as the distance of the vertex 416 from the x-axis 410along the y-axis 412. Also, a distance D2 can be defined as the distanceof the apex curve 408 from the x-axis 410 along the y-axis 412. Withthese example parameters defined, the rho value, also known as aprojective discriminant, can be defined as the ratio of the distance D1to the distance D2. The rho value can be defined for conic shapes andcan range in value between about 0 and about 1. In some instances, therho value can signify an ellipse if it is less than about 0.5, aparabola if it is equal to about 0.5, and a hyperbola if it is more thanabout 0.5. In other embodiments, the rho value can range in valuebetween about 0 and about 1.

In an aspect of the invention, providing one or more conic cuts 304 caninclude providing one or more conic cuts with an elliptical shape orsimilar geometry which corresponds to a rho value less than about 0.5and maintaining a depth ‘D’ of about 0.45 inches (11.4 mm), and a length‘L’ of about 0.55 inches (14.0 mm).

Referring back to FIGS. 3 a-3 e, another embodiment of the invention caninclude a method for repairing of a rotor disk 100 with one or morecracks 208, where one or more cracks 208 can be identified in aplurality of acute corners 206 of the forward side 112 of the base 102of the rotor disk 100. Further, the length ‘C’ of the one or more cracks208 can be greater than about 0.1 inches (2.5 mm) and within about 0.25inches (6.4 mm). Subsequently, the one or more cracks 208 can be removedacross a portion of the width 204 and/or depth 205 of the base 102 onthe forward side 112 of the rotor disk 100 to provide one or morefillets 302 on the base 102 of the rotor disk 100. In an aspect of theinvention, the radii ‘ΦR’ of one or more fillets can be about 0.1 inches(2.5 mm) and the depth ‘L1’ can be about 0.25 inches (6.4 mm). One ormore fillets 302 can be provided across the portion of the width 204 orthe depth 205 of the base 102, and along the circumference of the rotordisk 100.

In an aspect of the invention, one or more fillets 302 can be roundshaped and providing one or more fillets 302 on the base 102 of therotor disk 100 can include providing one or more fillets 302 with aradii ‘ΦR’ of about 0.1 inches (2.5 mm), and a depth ‘L1’ between about0.1 inches (2.5 mm) to about 0.25 inches (6.4 mm). However the radii‘ΦR’ and the depth ‘L1’ of one or more fillets 302, need not be limitedto these values, as one can suitably select a radii ‘ΦR’ and a depth‘L1’ of the one or more fillets 302 as per the applications of thecompressor rotor wheel assembly to remove the one or more cracks 208 inaccordance with an embodiment of the invention.

Further, one or more conic cuts 304 with an elliptical shape can beprovided between the pair of dovetail walls 202 a and 202 b of at leastone dovetail slot 104, on the forward side 112 of the base 102 of therotor disk 100. In an aspect of the invention, one or more conic cutscan have a depth ‘D’ of about 0.45 inches (11.4 mm) and the length ‘L’of about 0.55 inches (14.0 mm). In another aspect of the invention, oneor more conic cuts 304 can be provided on both the forward side 112 andthe aft side of the base 102 of the rotor disk 100. The method furthercan include installing the repaired rotor disk in the gas turbine.

FIG. 5 illustrates an example method for repairing a rotor disk inaccordance with an embodiment of the invention. In the embodiment shownin FIG. 5, a method 500 for repairing a rotor disk for reuse in a gasturbine can be provided. The method 500 can begin at block 502, in whichone or more cracks 208 are identified on a base 102 of a rotor disk 100.The length ‘C’ of one or more cracks 208 can be greater than about 0.1inches (2.5 mm) and within about 0.25 inches (6.4 mm). In one aspect ofthe invention, the cracks can be identified on at least a forward side112 or the aft side of the base 102 of the rotor disk 100.

Block 502 is followed by block 504, in which one or more fillets 302 canbe provided on the base 102 of the rotor disk 100 to remove one or morecracks 208.

In an aspect of the invention, one or more fillets 302 can be providedacross a portion of the width 204 or depth 205 of the base 102, andalong the circumference of the rotor disk 100. In another aspect of theinvention, one or more fillets 302 can be round shaped, and providingone or more fillets 302 on the base 102 of the rotor disk 100 caninclude providing one or more fillets 302 with a radii ‘ΦR’ of about 0.1inches (2.5 mm), and a depth ‘L1’ between about 0.1 inches (2.5 mm) toabout 0.25 inches (6.4 mm). However the radii ‘ΦR’ and the depth ‘L1’ ofthe one or more fillets 302 is not limited to these values, as one cansuitably select a radii ‘R’ and a depth ‘L1’ of the one or more fillets302 as per the applications of the compressor rotor wheel assembly toremove the one or more cracks 208 in accordance with an embodiment ofthe invention.

Block 504 is followed by block 506, in which one or more conic cuts 304can be provided between a pair of dovetail walls 202 a and 202 b in atleast one dovetail slot of the rotor disk 100. One or more conic cuts304 can be provided between the pair of dovetail walls 202 a and 202 bon at least the aft side or the forward side 112 of the base 102 of therotor disk 100 to facilitate or otherwise cause a relaxation of some orall of the tangential and/or radial stresses at some or all of theplurality of acute corners 206 of at least one dovetail slot 104.Relatively high stress values may adversely affect the life of the rotordisk 100 for use in service. Relatively lower stress values may increasethe life of the rotor disk 100. The crack initiation life is one measureof the life of the rotor disk 100. Therefore relaxation of some or allof the stresses can cause the crack initiation life of the rotor disk100 to improve and scrapping of the rotor disk 100 with one or cracks208 may be avoided or otherwise minimized.

In an aspect of the invention, one or more conic cuts 304 between a pairof dovetail walls 202 a and 202 b can include a depth ‘D’ of about 0.45inches (11.4 mm), and a length ‘L’ of about 0.55 inches (14.0 mm).However the depth ‘D’ and the length ‘L’ of tone or more conic cuts 304,are not limited to these values, since one can suitably select a depth‘D’ and a length ‘L’ of the one or more conic cuts 304 as per theapplications of the compressor rotor wheel assembly in accordance withan embodiment of the invention. To define the geometry of the one ormore conic cuts 304, a rho value also called projective discriminant canbe selected. The method of providing the one or more conic cuts 304 caninclude maintaining a rho (projective discriminant) value of the shapeor geometry of the cut to be less than about 0.5 and thereby controllingor otherwise determining the geometry of the one or more conic cuts 304to be elliptically shaped.

The method 500 ends after block 506. In other embodiments, an examplemethod can have fewer or greater elements, which may be performed in asimilar or different sequence than described above.

In an embodiment of the invention, a method of reusing a repaired rotordisk with one or more fillets 302 and one or more conic cuts 304 isprovided. After repairing the rotor disk 100, the rotor disk 100 can beinstalled in a gas turbine. In some instances, the repair can beperformed off site from the associated gas turbine and thus some or alltransportation cost of the rotor disk 100 may be minimized. The one ormore conic cuts 304 can be provided in the repaired rotor disk 100,which may reduce some or all tangential and/or radial stresses duringoperational or cold start conditions, which in turn can improve thecrack initiation life of one or more cracks 208 at some or all of theplurality of acute corners 206 of at least one dovetail slot 104.Embodiments of the invention provided are not limited to the repairmethod of the rotor disk of the gas turbine. One may recognize theapplicability of the repair methodology applied to a rotor disk 100 withthe at least one dovetail slot 104 can be applied in many similar rotorapplications including power generation and thrust generation. Aspectsof the invention can include the reduction of scrapping of a rotor diskwith one or more cracks at a plurality of corners. Furthermore, a repairprocess in accordance with an embodiment of the invention may berelatively easy to implement at an installation or a customer site.

The foregoing written description uses examples to describe variousembodiments of the invention. It will be recognized by those skilled inthe art that changes may be made in the above described embodimentswithout departing from the concepts thereof. The invention is notlimited to the particular embodiments disclosed, but is intended tocover all modifications within the scope of the application.

1. A method for repairing a rotor disk for a gas turbine, wherein therotor disk comprises a base and at least one dovetail slot between apair of dovetail walls, the method comprising. identifying one or morecracks on the base of the rotor disk; providing one or more fillets onthe base of the rotor disk by removing the one or more cracks; andproviding one or more conic cuts between the pair of dovetail walls ofat least one dovetail slot.
 2. The method of claim 1, further comprisinginstalling the repaired rotor disk in the gas turbine.
 3. The method ofclaim 1, wherein identifying one or more cracks comprises identifyingone or more cracks with a length greater than about 0.1 inches andwithin about 0.25 inches.
 4. The method of claim 1, wherein providingone or more fillets comprises removing one or more cracks across aportion of the width or depth of the base on an aft side of the rotordisk.
 5. The method of claim 1, wherein providing one or more filletscomprises removing one or more cracks across a portion of the width ordepth of the base on a forward side of the rotor disk.
 6. The method ofclaim 1, wherein providing one or more fillets comprises providing oneor more fillets with a radii of about 0.1 inches and a depth greaterthan about 0.1 inches and within about 0.25 inches.
 7. The method ofclaim 1, wherein providing one or more conic cuts comprises providingone or more conic cuts on an aft side of the rotor disk.
 8. The methodof claim 1, wherein providing one or more conic cuts comprises providingone or more conic cuts on a forward side of the rotor disk.
 9. Themethod of claim 1, wherein providing one or more conic cuts comprisesproviding one or more conic cuts with a rho value less than about 0.5.10. The method of claim 1, wherein providing one or more conic cutscomprises providing one or more conic cuts with a depth between about0.05 to about 0.45 inches, and a length between about 0.05 to about 0.55inches.
 11. A rotor disk for a gas turbine, wherein the rotor diskcomprises a base and the at least one dovetail slot between a pair ofdovetail walls, the rotor disk comprising: one or more fillets providedon the base of the rotor disk to remove one or more cracks from the baseof the rotor disk; and one or more conic cuts provided on the base ofthe rotor disk between the pair of dovetail walls of the at least onedovetail slot.
 12. The rotor disk of claim 11, wherein the one or morefillets comprise one or more cracks removed across a portion of a widthor depth of the base on an aft side of the rotor disk.
 13. The rotordisk of claim 11, wherein the one or more fillets comprise one or morecracks removed across a portion of a width or depth of the base on aforward side of the rotor disk.
 14. The rotor disk of claim 11, whereinthe one or more fillets comprise radii of about 0.1 inches and a depthgreater than about 0.1 inches and within about 0.25 inches.
 15. Therotor disk of claim 11, wherein the one or more conic cuts are providedon an aft side of the rotor disk.
 16. The rotor disk of claim 11,wherein the one or more conic cuts are provided on a forward side of therotor disk.
 17. The rotor disk of claim 1, wherein the one or more coniccuts comprise a rho value less than about 0.5.
 18. The rotor disk ofclaim 11, wherein the one or more conic cuts comprise a depth betweenabout 0.05 to about 0.45 inches, and a length between about 0.05 toabout 0.55 inches.
 19. A method for reusing a rotor disk for a gasturbine, the rotor disk comprising a base and at least one dovetail slotbetween a pair of dovetail walls, the method comprising: identifying oneor more cracks with a length greater than about 0.1 inches and withinabout 0.25 inches on the base; providing one or more fillets on aforward or aft side of the base by removing the one or more cracksacross a portion of a width or depth of the base of rotor disk, whereinthe one or more fillets comprise a radii of about 0.1 inches; andproviding one or more conic cuts on the forward or aft side of the rotordisk and between the pair of dovetail walls of the at least one dovetailslot, wherein the one or more conic cuts comprise a rho value less thanabout 0.5.
 20. The method of claim 19, further comprising: installingthe repaired rotor disk in a gas turbine.